Wood finishing



April 4, 1944. E. A. LEHMAN WOOD FINISHING Filed Dec. 17, 1941 IN V EN TOR.

Ed BY Patented Apr. 4, 1944 WOOD FINISHING Edgar A. Lehman, Mishawaka, Ind., assignor to The American Foundry Equipment Com Mishawaka, Ind., a corporation of Delaware Application December 11, 1941, Serial No. 423,321 20 Claims. (Cl. 117-101) This invention relates to wood finishing, and more particularly to the staining of wood surfaces to emphasize the grain structure and impart the desired color tone to the finished product.

In finishing wood trim, wood panels and furniture woods, it has been customary to stain thf wood with a liquid stain to impart the desired tone or color to the finished product. The stairn ing is applied either while the wood is still in board or strip form or after the wood has been assembled into the desired piece of furniture or other article.

In preparing wood surfaces for staining, it is generally customary to sand the surface to smooth the same. The sanding operation, however, partially loosens and raises minute fibers which project above the sanded surface. These projecting fibers are visible to the naked eye in certain soft woods, such as willow, basswood, poplar and cottonwood, as a fine fuzz projecting from the sanded surface. On the harder woods the partially loosened projecting fibers are also raised by the sanding but are less visible to the naked eye. Under present methods of wood finishing, it is necessary to sand the wood surface a second time after the first sealer coating has been applied to the surface. The first sealer coat appears to make the projecting fibers relatively brittle so that they are leveled or broken off by the second sanding operation without raising new loose fibers.

Porous woods, such as oak, walnut, beech, mahogany or hickory, are treated with a colored filling material to fill the pores of the wood either before or after staining and sanding. In many cases porous woods are first stained, the pores then filled with a colored filler, and the surface subsequently sanded.

All woods, whether soft, hard or porous, are now commonly stained with a liquid stain when the finished surface is to reveal the grain structure.

The liquid stain contains the desired coloring pigment which imparts the desired color to the finished wood along with a drier and a suitable vehicle. After the applied stain has thoroughly dried, a transparent finishing lacquer or coating is brushed or sprayed onto the finished surface. The transparent coating serves to protect the wood and stain from discoloration and damage and imparts a glossy finish to the treated wood.

It is desirable that the finished wood as used for furniture, trim and panelling, reveal the wood grain lines through the transparent lacquer holdly and distinctly. The planed surfaces of many woods before treatment do not reveal the grain lines distinctly or with emphasis. The liquid stains normally used fail to emphasize the wood grain in the planed or sanded wood surface for the reason that the vehicle portion of the stain which carries the pigment soaks more or less uniformly into the surface of the wood and blurs the grain lines, so that the stained product often possesses less visible grain emphasis than the planed or sanded unstained wood surface. When the final transparent lacquer coating is applied, the wood grain is therefore not emphasized to the desired degree but is often blurred and indistinct.

An object of this invention is to provide an improved method of staining wood whereby the grain lines are emphasized and enhanced to a greater degree than has been attained by any method heretofore practised.

Another object of this invention is to provide an improved method of staining wood which makes use of the physical characteristics of the wood itself to obtain grain emphasis.

Another object of this invention is to provide a mechanical method of staining wood by the use of dry pigment only and without the use of expensive oils or other pigment carrying vehicles and driers.

Another object of this invention is to provide an improved method of producing a smoother and finer finish on wood surfaces by removing the minute projecting fibers simultaneously during the staining operation.

The present application is a. continuation-inpart of my application Serial No. 298,071, filed October 5, 1939, and entitled Process of forming ornamented wood surfaces.

Another object of this invention is to provide a dry process of staining wood which is substantially more economical than present methods employing liquid stains, which can be performed more quickly and expeditiously, and which results in an improved finished product.

Another object of this invention is to provide a stained wood which has greater grain emphasis and tone quality than any product of like nature heretofore produced.

Other objects of this invention will become apparent as the disclosure proceeds.

Variousother features and advantages of the invention will be apparent from the following particular description and from an inspection of the accompanying drawing.

Although the novel features which are beplaned or sanded wood before treatment showing the natural grain lines therein;

Fig. 2 is a magnified cross-section of the wood showing the grain lines emerging into the planed or sanded surface of the wood;

Fig. 3 illustrates a number of particles of hard carrier granules greatly magnified, some of which are shown as coated with the selected color-ing,-

pigment;

Fig. 4 is a diagrammatic illustration of a centrifugal blasting wheel showing the manner in which the hard pigment-coated carrier particles are thrown from the periphery of the wheel to bombard the planed or sanded surface of the natural wood;

Fig. 5 is a magnified cross-section of the wood surface after bombardment, illustrating the manner in which the pigment has arranged itself on the wood surface;

Fig. 6 is a magnified plan view of the wood section showing the arrangement of the pigment on the bombarded surface thereof and wherein the pigment is deposited with greater density along the grain lines than between the grain lines;

Fig. 7 is a magnified plan view of the wood after the transparent lacquer or protective coating has been applied to the dry stained wood surface; and

Fig. 8 is a magnified cross-sectional view through the finished wood product after application of the transparent lacquer to the dry stained wood surface.

Similar reference characters refer to similar parts throughout the several views of the drawing and the specification.

The summer growth of the wood, which is generally characterized by darker grain lines, is harder or less resilient than the spring wood growth, usually identified in most woods with a lighter colored marking than the spring growth. I have discovered that the spring growth responds to particle bombardment to a different degree or measure than the summer wood. This characteristic of the wood growth is taken advantage of and made use of in my improved process of wood staining.

To illustrate more clearly my improved method. there is shown in Fig. 1 a short section of wood I whose top surface 2 has been sanded and coated with a sealer 2". The minute surface fibers indicated by the numeral 2 are shown in Fig. 2 projecting through the sealer coat 2". When porous woods are to be stained the pores are preferably filled with a suitable wood filler applied either before or after staining. As shown in Figs. 1 and 2, the summer growth portions, indicated by the numeral 3, are generally referred to as the grain lines of the wood, and the intermediate portions, indicated at 4, are generally referred to as the spring growths. I have found that the summer growth grain line portions 3 are harder or otherwise possess different characteristics than the intermediate spring growth portions 4. and respond in different degrees to particle Tbombardment. By taking full advantage of this natural characteristic, I am able to sharply develop and emphasize the grain characteristics of the wood, even though the planed untreated or sealer coated wood surface reveals the grain structure to the human eye only faintly.

In practising the invention, a very fine granular material is selected which is clean and hard and of such a nature that it will not discolor the wood. Metal abrasives can be used for the purpose .but it must be free from rust, surface dust or other foreign matter which would have a tendency to become deposited on the wood surface during bombardment action. Since the granular bombarding particles 5 as shown greatly magnified in Fig. 3, can be recovered and re-used time and again, granular particles can be economically selected which are clean and hard and do not discolor the wood. I have found that aluminum oxide or silicon carbide particles (car-borundum) or crucible steel grit are especially adapted for the purpose, since they are good carriers of the fine pigment, are clean and hard, and do not impart any of their color to the wood surface.

The granular carrier particles 5, such as aluminum oxide, silicon carbide (carborundum), or metal abrasive should be relatively fine and preferably should have a fineness of mesh or finer.

The powdered pigment 6 is mixed with the ranular carrier particles by stirring the carrier particles 5 and pigment powder 8 together. The pigment powder 6 will adhere to the surface of the granular carrier particles 5 and coat the same, as indicated in Fig. 3 where some of the pigment coated carrier particles are shown in cross section to more clearly reveal the pigment coating. The pigment selected may be the ordinary paint or stain pigment possessing the desired color, such as brown, amber, gray, red, orange, yellow, blue, violet, black, or shades thereof.

The amount of pigment powder which is mixed with the granular carrier particles determines the color denseness or tone of the finished product. To obtain a relatively light tone, for example, approximately one pound of color pigment is mixed with approximately pounds of granular carrier particles, such as aluminum oxide particles. Where a relatively solid, opaque finish is desired, the pigment powder can be greatly increased up to one pound of pigment to approximateiy two pounds of granular carrier particles, such as aluminum oxide particles. Thus the color depth or tone of the finished product can be varied within wide limits by properly proportioning the pigment powder and granular carrier mixture. For example, I have found that approximately 25 pounds of granular carrier material, such as aluminum oxide particles, mixed with one pound of brown or amber pigment powder will produce a highly acceptable brown or amber tone quality with full grain emphasis.

Where the lighter or pastel shade pigments areother factors, as hereafter brought out. are taken into account.

In carrying out my invention, the pigmentcoated carrier particles are fed into a bladed centrifugal throwing wheel, indicated generally by the numeral 1., and are thrown from the periphery of the wheel I under controlled conditions against the planed surface 2 of the wood to be treated. A centrifugal blasting wheel which I have successfully used for this purpose is illustrated in Unger Patent No. 2,162,139. The bombardment wheel I may be made in almost any desired size and is rotated at a peripheral velocity of approximately 4,000 to 14,000 lineal feet per minute. A wheel 1 of convenient size which I have successfully employed has a diameter of approximately fifteen inches and a blade width of 1 inches equipped with an apertured control cage to direct the fired material uniformly onto the wood surface. The lower periphery of a wheel of such size is spaced from 5 to 20 inches from the wood surface 2. The pigment-coated granular material 5-4 is fed into the central impeller positioned within the control cage and which rotates with the blades of the wheel. The impeller operates to throw the granular material out through the discharge opening in the control cage and into the path of rotation of the throwing blades. Such a wheel having a diameter of fifteen inches may be rotated from 1500 to 3600 R. P. M. depending upon the character of the wood being treated. For the treatment of most woods, a wheel of inch diameter rotated at 2500 to 3500 R. P. M. has proven satisfactory.

As illustrated in Fig. 4, the pigment-coated granular particles, designated as'5-6, are thrown at a velocity of 4,000 to 14,000 lineal feet per minute so as to bombard the planed surface 2 of the wood I. The pigment material 6 on the particles 5 is jarred from the carrier particles by the impact and are deposited upon the planed, sanded or sealer coated surface of the wood. The wood is kept constantly moving under the bombarding blast, so that approximately one pound of pigment-coated granular material is thrown against approximately one square foot of wood surface 2, which is suflicient to produce a clearly and distinctly defined grain structure. However, the quantity of pigment-coated granular material which may be thrown against a square foot of surface area may be varied somewhat but should not be reduced below one-half pound of pigmentcoated granular material per square foot of wood surface treated and preferably should not exceed three pounds of pigment-coated granular material per square foot of wood surface treated. Where the pigment is very dark the lesser amount of dark pigment-coated granular material may be bombarded against the wood surface than where the pigment has a lighter or pastel shade, in which event the relatively higher quantity of light colored pigment-coated granular material is bombarded against the wood surface. The abrasive throwing wheel I is so constructed that a substantial quantity of air is permitted to flow through the feed pipe and into the wheel. This air serves the useful function of assisting in distributing the pigment powder over the wood surfaces so as to obtain the most pronounced grain effects.

When the wood surface has been bombarded with the pigment coated granular material as above described, and in the quantities above referred to, it is found that the pigment becomes deposited on the wood surface 2 in varying denslty and in direct proportion to the grain growth. The denser quantity of pigment, as indicated at 6', is deposited along lines defined by the summer growth or grain lines of the wood, and the lesser amount of pigment powder 6" is deposited on the area defined by the spring growth. The reason for this resulting phenomenon is believed to be due to the varying physical characteristics of the spring and summer growths, such as the relative greater hardness of the summer growth as compared with the spring growth.

The impact and abrading action of the carrier granules 5 also removes all surface roughness and projecting wood fibers 2' remaining after the usual sanding operation. It will be noted that this is accomplished during the application of the dry pigment stain 6 without interfering with or delaying the staining operation.

I have also discovered that a. substantial portion of the pigment powder 6 which strikes the spring growth during the bombardment action bounds off or fails to adhere to the wood or sealer coat, or is blown off along with the minute wood fibers 2 loosened by the abrading action of the granules 5, and that the pigment particles striking the summer growth 3 adhere thereto to a greater degree or with greater intensity. Not only does the pigment powder 6 adhere in greater quantity to the summer growth areas 3 than to the spring growth areas 4, but the density of the pigment deposit is in direct proportion to the grain line characteristics of the wood and this holds true even though a sealer 2" has been applied to the wood. It further appears that the pigment does not appreciably penetrate the surface of the wood but forms a surface deposit which clings to the wood or sealer surface and does not readily shake off.

The planed, sanded or sealer coated surface of the woo-d is bombarded with the pigment-coated carrier particles for a very few seconds only as the wood is moved through the bombarding stream. As the bombardment progresses, the grain lines gradually emerge and become visible by reason of the varying density of the pigment deposit, until the point of optimum grain emphasis is reached. If bombardment is continued beyond this point the pigment deposit becomes more uniformly dense over the entire wood surface and the grain lines gradually fade or become less visibly distinct. Therefore, to achieve the most pronounced grain emphasis, it is important that the bombardment cease when the point of optimum grain emphasis has been reached, which point is visibly apparent. Usually the optimum grain emphasis is reached after each square foot of surface treated has been bombarded with from one-half to three pounds of pigment-coated granules 5-6 under the conditions above described. The grain emphasis can be readily controlled for a given mixture feed volume and a given speed of the wheel by the length of the bombardment period to which the wood surface is subjected, much the same as the .distinctness of a picture produced by the unrelated art of photography is determined by the period of time the film is exposed.

It will be appreciated that the speed of the wheel, the character and shape of the surface treated, the kind, quality and color of the pigment employed, and the rate of production desired, are determining factors in the selection of the quantity of pigment 6 to be mixed with the carrier granules 5 and the quantity of the mixture 5-6 to be thrown against each square foot of surface to be treated. Generally, however, one pound of a relatively dark but high-grade quality pigment is sufficient to satisfactorily stain from 50 to 150 square feet of surface, while one pound of relatively light color pigment may be required to satisfactorily stain from 10 to 50 square feet of surface. I

It has been found that a centrifugal projector wheel employing a control cage and impeller and amply ventilated as illustrated in Unger Patent No. 2,162,139, produces the most perfect grained surface. Air blast projection of the pigmentcoated carrier particles is not recommended if the best product is to be produced. The usual air blast nozzles appear to throw the pigment-coated carrier particles with less uniformity and the excessive amount of air employed appears to disturb the pigment deposition so that the pigment deposit does not so accurately portray the grain lines. In addition to being more adaptable for the purpose, the centrifugal bombardment wheels produce greater production output and are less expensive to operate than the air blast nozzles.

By this method of depositing dry pigment, the

grain lines can be visibly emphasized with a distinction substantially greater than is apparent from a visual inspection of the planed untreated wood. Thus woods which have no clearly visible grain can be treated so as to produce a finished article with a very definite and pronounced grain. No process heretofore known, no matter how costly or complicated, can produce the rain emphasis which can be inexpensively produced by this process.

Not only can the grain structure be emphasized to a remarkable degree with this process, but grain emphasis can be reduced or toned down merely by the expedient of reducing or increasing the bombardment period. Any desired wood coloring, grain emphasis and tone can be produced with a given wheel feed and wheel speed by the simple expedient of selecting the desired color pigment, mixing the pigment in proper proportions with the granular carrier material and regulating the bombardment period. The pigment powder deposited upon the wood surface firmly adheres thereto and will not shake off. It can only .be partially removed, obliterated or blurred by rubbing. r

The pigment powder deposited on the wood surface is bonded in place and the wood given its final finish by spraying any selected transparent lacquer or transparent coating 8 thereon. No especial care need be taken in spraying the transparent lacquer coating to the pigmented wood surface since the pigment cannot normally be blown or shaken off during the lacquering operation and is in no way disturbed by the application of the lacquer. The pigment deposited on the wood surface will clearly and distinctly reflect the wood grain demarcations through the transparent lacquer. A stained wood product which is fully as serviceable and long wearing as any heretofore produced, can thus be made.

My improved process for staining wood produces a product of greater uniformity and much more pronounced grain lines than can be produced by any methods heretofore known. By my process the coloring pigment is applied dry and the entire cost of the expensive vehicles and driers employed in liquid stains is entirely saved.

All fibers 2' projecting from the sanded surface are removed by the carrier granules as the staining operation proceeds. The pigment deposition and the desired grain emphasis is in no way affected by the sealer coat 2" that may have been previously applied to the wood surface.

Ahnost any desired production speed may be obtained by employing the desired number of centrifugal bombarding wheels. For example, one bombarding wheel having a diameter of fifteen inches and throwing approximately six pounds of pigment-coated granular particles per minute will stain from six to eight feet of wood surface per minute. Relatively large or high capacity bombardment wheels I throwing as high as to 200 pounds of pigment-coated granular particles 5-6 per minute may be employed, whereby 50 to 100 square feet of surface may be eifectively stained per minute. By increasing the wheel feed, by employing a large capacity wheel, or by employing a plurality of wheels, it is apparent that almost any desired staining speed may be attained. The transparent lacquer coat can be applied immediately after the dry staining operation, as by spraying, without interfering with high speed production.

While certain novel features of the invention have been disclosed and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes may be made by those skilled in the art without depart ing from the spirit of the invention.

What is claimed is:

1. The process of emphasizing the grain structure of wood which includes, bombardingt e wood surface with hard granular particles which per se will not discolor the wood, the particles being coated with dry pigment powder, until the wood grain lines are revealed by the pigment deposition.

2. The process of emphasizing the grain structure of wood which includes, bombarding the wood surface with hard granular particles which per se will not discolor the wood, the particles being coated with dry pigment powder so as to deposit the pigment powder on said surface in denisities which vary with the density of the wood gra n.

3. The process of staining wood surfaces which includes, coating clean, hard, irregular particles with a dry pigment powder, and bombarding the wood surface with the pigment-coated particles until the wood grain lines are revealed by the pigment deposition.

4. The process of staining wood surfaces which includes, coating clean and hard, irregular particles with a dry pigment powder, bombarding the wood surface with the pigment-coated particles until the wood grain 1ines are revealed by the pigment deposition, and coating said pigmented surface with a transparent lacquer to bond the deposited pigment to the wood.

5. The process of staining wood surfaces which includes, coating clean and hard aluminum oxide particles with dry pigment powder, and bombarding the wood surface with the pigmentcoated particles until the wood grain lines are revealed by the pigment deposition.

6. The process of staining wood surfaces which includes, coating clean and hard silicon carbide particles with dry pigment powder, and bombarding the wood surface with the pigmentcoated particles until th wood grain lines are revealed by the pigment deposition.

7. The process of staining wood surfaces to emphasize the grain growth which includes, centrifugally projecting relatively fine and hard granular particles which per se will not discolor the wood, the particles being coated with dry pigment powder, against the wood surface so as to deposit the pigment powder on said surface in densities which vary with the density of the wood rain.

8. The process of emphasizing the grain structure of wood which includes, centrifugally proiecting relatively fine granular hard particles which per se will not discolor the wood, the particles being coated with dry pigment powder, against the surface of the wood at velocities of from 4,000 to 14,000 lineal feet per minute, and continuing said bombardment until the wood grain lines are revealed with optimum emphasis.

9. The process of emphasizing the grain structure of wood surfaces which includes, centrifugally projecting from one-half pound to three pounds of relatively hard and fine granular particles which per so will not discolor the wood, the particles being coated with dry pigment powder, against each square foot of the surface of the wood so as to deposit the pigment powder on said surface in densities which vary with the wood grain.

10. The process of emphasizing the grain structure of wood surfaces which includes, mixing clean and hard particles which per se will not discolor the wood, the particles being of 80 mesh or finer, with a dry pigment powder in the proportion of one pound of pigment powder to from two pounds to 150 pounds of said particles so as to coat said particles with the pigment powder, and centrifugally projecting from one-half pound to three pounds of the pigment-coated particles against each square foot of the surface of the wood so as to deposit the pigment powder on said surface in densities which vary with the wood grain.

11. The process of emphasizing the grain structure of wood surfaces which includes, mixing clean and hard particles which per se will not discolor the wood, the particles being of 80 mesh or finer, with a dry pigment powder in the proportion of one pound of pigment powder to from two pounds to 150 pounds of said particles so as to coat said particles with the pigment powder, centrifugally projecting from one-half pound to three pounds of the pigment-coated particles against each square foot of the surface 01' the wood so as to deposit the pigment powder on said surface in densities which vary with the wood grain, and coating said pigmented surface with a transparent lacquer to bond the deposited pigment to the wood.

12. A wood product having the natural grain thereof emphasized by a dry Pi ment deposit on the surface of the wood. wherein each surface element of the wood carries a coating of pig ment particles, the density of such pigment coating on each surface element varying in accordance with the relative density of the growth bands.

13. A wood product having the natural grain in the surface thereof emphasized and developed by a continuous and unbroken deposit of dry pigment on each surface element of the wood suriace, the density of said pigment deposit varying in direct proportion to the relative density of the spring growth and summer growth bands of the wood.

14. A finished wood product havingthe natural grain thereof emphasized by a dry pigment deposit on the surface of the wood, wherein each surface element of the wood carries a coating of pigment particles, the density of such pigment coating on each surface element varying in accordance with the relative density of the growth bands, and a transparent coating covering the pigmented surface and bonding the pigment deposit to the wood.

15. The process of highlighting, coloring and enhancing the appearance of grained wood including air blasting the wood surface with a mixture of relatively dry abrasive and coloring pigment until the wood grain lines are revealed by the pigment deposition.

16. The process of highlighting, coloring and enhancing the appearance of grained wood including centrifugaliy projecting onto the surface of said wood a mixture of relatively dry abrasive and coloring pigment until the wood grain lines are revealed by the pigment deposition.

17. A process, as defined in claim 15, characterized by coating the air blasted wood surface with a transparent lacquer.

18. A process, as defined in claim 16, characterized by coating the surface upon which the mixture of relatively dry abrasive and coloring pigment has been centrifugally projected, with a transparent lacquer.

19. A process of highlighting, coloring and enhancing the appearance of grained wood including bombarding the wood surface with a mixture of relatively dry hard granular particles and col- 'oring pigment, and coating said surface with a transparent lacquer.

20. A process of highlighting, coloring and enhancing the appearance of grained wood including centrifugally projecting onto the surface of said wood a mixture of relatively dry hard granular particles and coloring pigment, and coating said surface with a transparent lacquer.

EDGAR A. LEI-IMAN. 

